Amplifying system



Jan. 24, 1933. J ENGLV 1,895,152

AMPLIFYING SYSTEM Filed June 19, 19.30 2 Sheets-Sheet 1 INVENTOR Josef'zgl Y Jan. 24, 1933. J, ENGL 1,895,152

AMPLIFYING SYSTEM Filed June 19, 1930 2 SheetS-Sheet 2 N M @EQ lNVENTOR ATTORN EYS Joslin ENGL, or BERniN-GRUNEWLD';GERMANY, AssIGNoR Patented Jan. 24, 1933 roitkATIoN,` oF NEW YORK,y n n., A coRPoRAirroN oF `nnw` Yeux iU-IFYING SYSTEM Application med Jane 19,193o,`fseria1 Naf.' 462,199, andni Germany February 4, 192e.

' An applicationfor this invention' has been filed in Germany, Feb;4, 1929. l K v My invention relates to'amplifying' systems including a plurality of vacuum tubes.; v l My invention relates particularly-'to a system of the character described wherein distor- Y tion of the amplified current is less than exists v with prior arrangements.. g A v Various other objects, advantages and characteristics of my invention will become apparent from the followingdetailed description taken in connection witli the accompanying drawings;- Y f Q- t 1 My invention resides in the system, circuit arrangements and features v,of the character hereinafter describedand claimed. l

y For an understanding of Amy' inventionand for an illustration of some of the various formsthereof, reference isftobe had to the accompanying drawings, invwhich: r, 1 Figsifl and 2 are graphical Views of current oscillationsyand` 1 :Y :.w

Fig. 3 isa diagrammatic view of-an; amplilfying system4 arrangedflin faccordance `with Inyinvention. VIt is known inzthe'art 'that the anodecirfcuit ofeach vacuum tuberin'vanamplifying system may include an ohmicresis'tance or a "choke coil and that, upon occurrence ofcurrentY variations in an anode circuit of ,anyfgiven tube, voltage 'uctuations result between `the cathode andanode, of that tube, such voltage fluctuationsbeingl due to the varying voltage drop across the aforesaid ohmic" resistance or to the inductance of the choke-coil', as the case .may be.A With the grid ofthe; nextsucceeding amplifying tube connected-to the anode y of the aforesaid giventubethro'ugh a `coupling capacity, it has been customary to place a high ohmic resistance, known as a'lakage resistance, between :the 'grid' 'andzcathode of said succeeding amplifying tube, for example,

in seriesl with the 'grid 'biasingbattery, orl

equivalent, and' serving: to givexaafavorable working potential-tothe gridbf said succeeding amplifying tubej,`

' As regardsthe values ofithe aforesaidcoupling capacityand,leakagerresistance, the followin'g'holds' 'true 4As-flarg'e a- 4fraction `as possible of the alternating .voltage produced bye-*said given amplifying tube shouldbe'come To ENGL ritonucrs'coneffective between the cathode and gridof said next succeeding amplifying tube.' For this l purpose and for the frequency to be amplified,

the` impedance of the coupling condenser, which ata frequency'f and with a capacity G of the coupllng condenser has the value must be small. Preferably, it amounts to 13;; of the leakage resistance, and 90% ofthe. alternating voltages producedin saidv given amplifying tube act upon the next succeeding amplifying tube." If this relation is used as a basis for the choice of the coupling capacity andthe olimic leakage resistance for each frequency, there results Vfor the time constant T of the discharge ofthe coupling condenser,

Which'asis known isfequal `to the product of the ,coupling -capacity C andthe leakage l'resist-l ance w, a ligure, which isdependent onthe frequency and which is proportionately large for small frefquel'lcies.y f If the impedance of the couplingcondenser `is 116 ofthe leakageresistance'w, then thereis obtained foi-the time constant the proportionately vlargeamount of `Ol second.

This signifies the followingfor the mode of operation of amplifying systems of this kind:

Y f jIf., these. amplification `vl`stages are`4 fully modulatediby a higherV frequency, i Ifor "example, f=1000, `the couplingfcapacityas a Y consequence of the large time constant of the combinationdoes no have time to discharge again.l The consequence'o-f this is,r that "the mean grid bias changes and, -tlierefoie,the

amplification .stage at this high frequency is overmodulated.

' In accordance with my invention, the dis advantage thus recited asariSIlg in connection with capacity-coupledamplifying tubes is overcome byusing, a chokecoil as leakage resistance ,for 'the .last amplifying stage, the direct ycurrent resistance of` said choke coil 1 being so small that, together with the coupling vc'apaci1ty, there results time COIStant which does not 'exceed 'approXiinately'OOl of a second..l Since the impedance of: the choke 1coil may be large despite its low direc'tcun` A rent resistance, it results that good efficiency Y of operation, especiallyat low frequencies, is

Y obtained foro the tube forming "said last named amplifying stage.

` Referring to the drawings, Figs. 1 'and 2 show ygraphicallyv the modulation process of the anode current in the last amplifying stage at a high frequency where"f=1000, for eX- ample, which is the casey where the time con- Y* stant of the combination-coupling capacity soV and leakage resistance-is too large. As shown, themean anode current immediately rises and an oscillation supplied in sine form in the anode circuit, 1, ceases to have the sine form since substantial distortion takes place as shown in Fig. 2. 1

In general, the foregoing action 4occurs in the anode circuit of the last tubeofan amplifying system. However, in many cases, it-

mayoccur, in the event of appearance of sufficiently Vlarge modulation amplitudes, in o a preceding tube, forexample, the lasttube but oneof ,the amplifying system., Ordinarily, with all tubes kofthe system, except thelast two tubes, this phenomenon dees notY occur since, with them, Vthe controllable rangeis large in. contrast with the modulation ampli- F or purposes bffurther:eiiplanation ofvm'y invention, there ,is'pillustrated in Fig. 3 a

vacuum tube amplifying system of a particular type'although it shall be understood that my invention'isapplicable as wellto other c types of vacuum tube amplifying systems.

As shown, a plurality of V.vacuum tubes V, V1 and V2 are utilized'to form the last three stages of* a. multistage amplifying systenn'the u individual stages being connected'tofone a'nother infany suitablemanner, as, in the known way, by the` coupling resistances 1, 2 and 3 together with thervcoupling capacitiesvll, 5 and 6. Y Y i The filaments of the'aforesaid tubes land Vthe anode circuits thereof may 'be energized in anysuitable manner vsir'nilarly, the 'tem- Yporarily necessary grid*l biasing potentials maybe obtained in anysuitable'manner. lAs illustrative 'of Va fsiinple VA'arraiigen'ient, there Y Y. is herein shown a :filament battery 7,-a comvmonan'ode circuit V'battery 8, and the batteries 9,10 and 11 for V'aliiplying a biasing ipotentialto' the grids of fthe respective tubes VYunder some circumstances.

V, V1 and V2, all of said batteries being conne'cted in proper circuit relation as well under- Y stood in the art. It shall be distinctly understood that any other suitable energizing and grid-biasing arrangement 'may be utilized in lieu of that just described".

' In accordance wth usual practice, the grid circuiuofthe vacuum tube V includes an lohniic ;leakag'earesistance 12 and, in accord,- ance 'with my invention, theV grid circuit of the vacuum tube' V2 inclu'des'a choke coil 13 of 'flowohmic' resistance. Further, in accord-V ance `with my invention, the grid .circuit of degree of amplicati'on,the impedance 'of the aforesaidchoke coils 13 and/or'll `may-be made adjustable ina/ny suitable manner. To this end and as shown the choke -coil13 lmay comprise a. plurality of windings, one of which is connected to a 'suitable source lof direct fcurrent whereby, by a premagnetizing action, ythe vchoke coil impedance lmay be Y varied'in a desired adjustable manner. VThe chokecoil 14, when utilized, may be similarly which a sourceof 'current'is "connected:

Furthermore, 'to 'obtain a high'erfim'pe'dance withbutfew windings, vone or both fof the equipped with a supplementary.winding'to y cli'okeJfeoils13a1id $14 may be prov-ided with a'core or lcores 'of' magnetic "material .prefer ably having `high Iinitial permeability, such Y as permalloy :or other -materialsV yof 'similar properties. t .e v L AStill further,y the choke Vcoil core, when utilized, 'may be made adjustable `ordisplace'- 'able whereby the lchoke rcoil `impedance may be readily adjusted.- i

.f fIt-sha'll-be v:distinctly understood that 'my invention "contemplates the utilization of a choke coil, or equivalent, for but koneof 'the vacuum tubes, Iusually the last stage vacuum tube, of'the amplifying system although, if

desirable and necessary, one or more of the preceding amplifying tubes lmay be'similarly equipped.V Y 1 o 'Y y' Whilethe invention has been' described with ,respect "to certainv particular vpreferred examples which .give Y`satisfactory results, itf

will be understood by those skilled fin theart after `understanding' the invention, that variy ous changes and .modifications jmay be 'made -without'departlng from the spirit and 4scope rofthe' invention and vit fisfintended therefore in the appended claims to cover all suchv changes and modifications.

What is claimed as new and desired to be securedby Letters Patent is: l

1. In an amplifying system, a plurality of vacuum tubes, a connection including acapacity coupling between the anode of one tube and the grid of the next succeeding tube, a leakage path connected to said connection,

said leakage path including a choke coil of relatively low ohmic resistance and high im pedance, and a core of magnetic material for" said choke coil, said core being of high in-l itial permeability and adjustable whereby the impedance of said choke coil may be ad j usted.

2. In an amplifying system, a plurality of' vacuum tubes, a connection including a ca-l Y pacity coupling between the anode of one tube` and the grid of the next succeeding tube, a'- leakage path connected to said connection, said leakage path including a choke coil, and.

a magnetizing coil inductively related to said.

choke coil.

3. In an amplifying system, a plurality of vacuum tubes, a connection including aca pacity coupling between the anode of one tube and the grid of the next succeeding tube, a leakage path connected to said connection, said leakage path including a choke coil, a magnetizing coil inductively related to said Y choke coil, and a source of direct current connected to said magnetizing coil.

In testimony whereof I have `signed my name to this specification.

JOSEF ENGL. 

